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From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     Andy Lutomirski <luto@amacapital.net>,
        Boqun Feng <boqun.feng@gmail.com>,
        Will Deacon <will@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Waiman Long <longman@redhat.com>,
        Sultan Alsawaf <sultan@kerneltoast.com>,
        Theodore Ts'o <tytso@mit.edu>,
        Andy Lutomirski <luto@kernel.org>,
        Jonathan =?utf-8?Q?Neusch=C3=A4fer?= <j.neuschaefer@gmx.net>,
        LKML <linux-kernel@vger.kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH v3] random: remove batched entropy locking
Message-ID: <Yf1M3YGVq71oC9BM@linutronix.de>
References: <CAHmME9pO41uwYExSROc5X2+RE=a5tZfE=c=bAxVbhCHfa7=zSA@mail.gmail.com>
 <20220204155142.56419-1-Jason@zx2c4.com>
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On 2022-02-04 16:51:42 [+0100], Jason A. Donenfeld wrote:
> index 455615ac169a..3e54b90a3ff8 100644
> --- a/drivers/char/random.c
> +++ b/drivers/char/random.c
> @@ -1759,41 +1762,54 @@ u64 get_random_u64(void)
>  	unsigned long flags;
>  	struct batched_entropy *batch;
>  	static void *previous;
> +	int next_gen;
>  
>  	warn_unseeded_randomness(&previous);
>  
> -	batch = raw_cpu_ptr(&batched_entropy_u64);
> -	spin_lock_irqsave(&batch->batch_lock, flags);
> -	if (batch->position % ARRAY_SIZE(batch->entropy_u64) == 0) {
> +	batch = this_cpu_ptr(&batched_entropy_u64);
> +	local_lock_irqsave(&batch->lock, flags);

Does this compile and work? From the looks of it, this should be:

	local_lock_irqsave(&batched_entropy_u64.lock, flags);
	batch = this_cpu_ptr(&batched_entropy_u64);

and we could do s/this_cpu_ptr/raw_cpu_ptr/

Sebastian